1. Field of the Invention
The invention relates generally to apparatus for supplying highly saturated or wet steam to a treatment chamber, such as is contained in a closed vault. More particularly, the invention relates to novel but relatively simple apparatus for use with conventional steam boilers in industrial plants and the like, which produce dry or low moisture content steam, to enable such steam to be converted into highly saturated steam. The present apparatus automatically blends water with the steam from such boiler in controlled proportions, to produce highly saturated steam having a substantially constant moisture content, and a substantially constant pressure. Thus, existing plant facilities can be adapted to provide a form of steam for processing materials that could not be satisfactorily or efficiently processed with the previously available steam.
2. Description of the Prior Art
The satisfactory treating of some materials or objects in a steam treatment vault frequently requires the use of wet steam having a moisture content of say from 20% to 70% by weight. The steam boilers commonly available in a factory or mill are usually designed to produce dry steam, i.e., steam with little or no moisture content. Hence, these available steam supply sources cannot be used directly to supply wet steam to a treatment vault requiring such steam.
There is obtainable, commercially, specially designed steam generator units capable of supplying wet steam of a desired moisture content at a desired pressure, and such are presently used to supply treatment vaults where wet steam is necessary. However, where a new need arises for wet steam, due to changes in processes or installation of new equipment, and there is already available a supply of dry steam, it is more economical to utilize the existing facilities instead of acquiring a special new steam generator. Prior efforts have been made to provide adjunct devices to be used with such available facilities, but these have not proved reliable, or respond slowly, or require constant manual adjustment and attention, rendering them impractical. The present invention is directed to adjunct apparatus that can be installed for this purpose, and will operate automatically and satisfactorily.
The treatment process performed in a steam vault frequently requires wet steam of a specific, substantially constant, high moisture content, supplied at a constant rate and pressure, and preferably without off-quality or time lag, whenever there is a demand. The commercially available steam generator units specially designed for this purpose can meet these requirements, but prior to this invention there has been no known auxiliary apparatus capable of automatically converting available dry steam and water into a supply of wet steam of a given constant high moisture content, at a given constant pressure and volume, on instant demand.
One example of a process requiring wet steam involves the treatment of logs to prepare them for peeling in a lathe designed to cut sheets for use as veneer or for plywood. It has been found, according to a new process forming no part of the present invention, that by treating logs of a given specie of wood with wet steam having a moisture content of from 20% to 70% by weight, and preferably about 55% by weight, and under a pressure of 40 to 100 psig, and preferably about 60 psig, for a prescribed period of time, the wood fibers can be made relatively uniform in texture by heating and moisture saturation so that alternating bands of soft and hard growth, knots and the like will not interfere with the peeling of uniform sheets from the log by the lathe. The steam supply is automatically controlled in accordance with variations in the condensate temperature draining from the vault. The vault utilized to treat such logs is usually quite large, with typical dimensions being approximately 75 feet long, 14 feet high, and 12 feet wide, the vault being stacked substantially full of short 8 1/2 foot long logs for each treatment cycle. A typical plywood mill will have several such vaults, and thus, with the improved process, there is a demand for great quantities of wet steam.
The typical plywood mill operating under prior methods of steam treating logs has available dry steam and water in abundant supply, and hence it would be most economical if the available supply could be utilized to vaporize the treatment vaults to treat the logs in accordance with the improved, highly saturated steam process. In order to accomplish this, apparatus is provided in accordance with the present invention to blend water with the available dry steam in such a way as to produce wet steam of the desired constant, high moisture content, at the desired constant, volume and pressure, immediately upon demand.